1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to an ink-jet printhead having an improved structure in which a placement of heaters improves performance and life span of the printhead.
2. Description of the Related Art
Typically, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of printing ink at a desired position on a recording sheet. Ink-jet printheads are largely categorized into two types depending on which ink droplet ejection mechanism is used. A first type is a thermally driven ink-jet printhead in which a heat source is employed to form and expand bubbles in ink causing ink droplets to be ejected. A second type is a piezoelectrically driven ink-jet printhead in which a piezoelectric material deforms to exert pressure on ink causing ink droplets to be ejected.
Hereinafter, the ink ejection mechanism in the thermally driven ink-jet printhead will be described in greater detail. When a pulse current flows through a heater formed of a resistance heating material, the heater generates heat and ink adjacent to the heater is instantaneously heated to about 300° C., thereby boiling the ink. The boiling of the ink causes bubbles to be generated, expand, and apply pressure to an interior of an ink chamber filled with ink. As a result, ink near a nozzle is ejected from the ink chamber in droplet form through the nozzle.
The thermal driving method includes a top-shooting method, a side-shooting method, and a back-shooting method depending on a growth direction of bubbles and an ejection direction of ink droplets.
The top-shooting method is a method in which the growth direction of bubbles is the same as the ejection direction of ink droplets. The side-shooting method is a method in which the growth direction of bubbles is perpendicular to the ejection direction of ink droplets. The back-shooting method is a method in which the growth direction of bubbles is opposite to the ejection direction of ink droplets.
The ink-jet printheads using the thermal driving method should satisfy the following requirements. First, manufacturing of the ink-jet printheads should be simple, costs should be low, and should permit mass production thereof. Second, in order to obtain a high-quality image, crosstalk between adjacent nozzles should be suppressed while a distance between adjacent nozzles should be narrow; that is, in order to increase dots per inch (DPI), a plurality of nozzles should be densely positioned. Third, in order to perform a high-speed printing operation, a period in which the ink chamber is refilled with ink after ink has been ejected from the ink chamber should be as short as possible and the cooling of heated ink and heater should be performed quickly to increase a driving frequency.
FIG. 1 illustrates a partial cutaway perspective view schematically showing a structure of a conventional ink-jet printhead using a top-shooting method. FIG. 2 illustrates a cross-sectional view of a vertical structure of the ink-jet printhead of FIG. 1.
Referring to FIG. 1, the conventional ink-jet printhead includes a base plate 10 formed by a plurality of material layers stacked on a substrate, a barrier wall 20 that is formed on the base plate 10 and defines an ink chamber 22, and a nozzle plate 30 stacked on the barrier wall 20. Ink is filled in the ink chamber 22, and a heater (13 of FIG. 2), which heats ink and generates bubbles, is installed under the ink chamber 22. An ink passage 24 is a path through which ink is supplied to an interior of the ink chamber 22. The ink passage 24 is in communication with an ink reservoir (not shown). Each of a plurality of nozzles 32, through which ink is ejected, is formed in a position corresponding to each ink chamber 22.
The vertical structure of the ink-jet printhead described above will be described in connection with FIG. 2.
An insulating layer 12 for providing insulation between a heater 13 and a substrate 11 is formed on the substrate 11, which is formed of silicon. The heater 13, which heats ink in the ink chamber 22 and generates bubbles, is formed on the insulating layer 12. The heater 13 is formed by depositing tantalum nitride (TaN) or tantalum-aluminum (TaAl) on the insulating layer 12 in a thin film shape. A conductor 14 for applying a current to the heater 13 is formed on the heater 13. The conductor 14 is made of a metallic material having good conductivity, such as aluminum (Al) or an aluminum (Al) alloy.
A passivation layer 15 for passivating the heater 13 and the conductor 14 is formed on the heater 13 and the conductor 14. The passivation layer 15 prevents the heater 13 and the conductor 14 from oxidizing or directly contacting ink and is formed by depositing silicon nitride. In addition, an anti-cavitation layer 16, on which the ink chamber 22 is to be formed, is formed on the passivation layer 15.
The barrier wall 20 for forming the ink chamber 22 is stacked on the base plate 10, which is formed of a plurality of material layers stacked on the substrate 11. The nozzle plate 30, in which the nozzles 32 are formed, is stacked on the barrier wall 20.
In the ink-jet printhead having the above structure, the anti-cavitation layer 16, which is formed on the passivation layer 15, prevents damage to the heater 13 due to a cavitation pressure generated during bubble collapse. However, formation of the above-described anti-cavitation layer 16 on the passivation layer 15 presents complications to the manufacture and operation of the ink-jet printhead. Specifically, such an arrangement increases the number of printhead manufacturing processes and prevents heat generated by the heater 13 from being sufficiently transferred to ink.
In order to increase the life span of a heater, an ink passage has been formed with an asymmetric structure so that cavitation occurs in another location other than the location of the heater or cavitation is distributed over a wider area to reduce a pressure thereof.
FIG. 3 illustrates a plan view of a structure of a conventional ink-jet printhead. Referring to FIG. 3, the ink-jet printhead has an asymmetric structure in which a heater 50 and a nozzle 52 are positioned off-center with respect to an ink chamber 54. An ink passage 56 supplies ink to an interior of the ink chamber 54.
The above structure causes a variation in a flow of ink to the ink chamber 54. As a result, damage to the heater 50 caused by bubble collapse is decreased.
However, in the ink-jet printhead having the above asymmetric structure, the linearity of ink droplets ejected through the nozzle 52 is lowered, and the flow of fluid disturbing an ink refill operation occurs. As such, a driving frequency of a printhead is reduced.